The present invention relates to tools for borehole applications, in particular oil wells, gas wells or water-wells, more particularly including installations for primary, secondary or tertiary oil production, whether holes for injecting water, gas or another pressurizing agent (injector holes) or oil extraction (production wells). A particular application of the tool is in injector and producer multi-zone wells where the number of isolation zones is high and/or the wellbore casing is damaged or diverted, to quickly and economically isolate areas with damaged casing.
The present invention applies to tools carrying a packer device comprising seals mounted to a mandrel and forming with other operational components a tubing string (or just “tubing”) of tools and components joined one after another for lowering down a multifunctional (or multizonal) well, i.e. having multiple layers or strata which should be isolated from one another. Packer tools are not unusual in the oil industry. The tubing string comprising a number of function-specific tools is lowered into a well, maintaining an annular space between the tubing string and a well casing.
Packer tools generally comprise two basic elements: packer seals for isolating annular regions thereabove and below and anchor slips to affix the tool to a point of the casing. A packer sealing element is a ring made of metal and typically dense synthetic rubber that fits around the tubing in a well. The packer seal (the “packing element”) of a packer tool (the “packer”) is typically a rubber ring that expands against the side of the casing lining the side of the wellbore. A packer may, and usually will, have more than one packing element. In the majority of active wells in the world today, this tubing is used to either produce oil or gas out of the well and serve as a conduit to transport water into the well for water injection and waterflood applications. The packer provides a secure packer seal between everything above and below where it is set. The main reasons for using a packer are to keep sediment, sand and other potentially corrosive or erosive materials from flowing into the annulus and damaging the casing, and to control the zone of the well from which hydrocarbons are being produced in a producer well or to control the zone where water is being injected in an injection well.
Slips hold the packer in place and prevent them from moving once they are set in the well. A slip is a serrated piece of metal that grips the side of the casing. Some packers lack a specific anchor device (in which case they are known as packer-tandems).
Insofar as the present invention is concerned, the packer tool sequentially carries out the following phases:
Run-in: The tubing enters the well and the packer is lowered down to a set position.
Setting: Both the anchor slips and the packer seals are pushed outwards to respectively clamp the tool to the well while the tubing is down the well, isolating annular regions above and below the packer. The tool setting system may be mechanical, involving rotation or axial compression or traction, or else hydraulic by injecting a pressurizing fluid.
Release: This operation is carried out on removable tools to unset them from the well casing in order that they may be extracted. In tools having release systems, known as removable packers, release may be based on similar maneuvers or a combination thereof. Tools lacking a release system are known as permanent packers which need to be rotated to literally destroy the tool by machine milling. This operation is costly and time-consuming.
Extraction: The removable packer is hauled up to the mouth of the well.
The invention particularly relates to a packer tool that is removable, hydraulically set and mechanically released.
The present invention concerns the packer tool anchoring means to the well casing wall by means of a dual-grip anchor device having bidirectional anchor slips, more precisely the release of the anchor slips.
Use of mechanically- or hydraulically-actuated packer tools or, simply, packers for maintaining separation between production layers or fluid injection layers is well known in the oil industry.
The best known release systems are by rotation and traction. In the first system, the tool is released by rotating it several turns, which complicates the operation the deeper in the well because of the greater number of tools. This in turn makes the operation unreliable through uncertainty regarding which tool is actually being operated.
In traction release, tractive tension is applied to the piping to shear a number of brass or steel pins. Once set, this kind of tool is subject to stress from temperature and pressure variations down the well, which get worse with increased depth to the point that pins may shear producing accidental tool release.
Also known in the art is to provide packer tools with an anchor device to affix the tool to the well casing wall for the duration in which the tool will remain inside the well for operations. U.S. Pat. No. 4,156,460 discloses a removable packer with two separate sets of slip teeth with a seal device in between. Each set comprises four anchor slips at 90° from one another around mandrel. The upper set has its teeth facing upwards to selectively anchor the tool against upwardly movement whereas the teeth of the lower anchor slips face down in the opposite direction to selectively hold the tool against downwardly movement. Each set is engaged by its own actuator cone.
CA patent 2,286,957 illustrates the known concept of integrating the teeth of anchor slips in pairs, each pair consisting of one set of teeth directed against upward movement and another set of teeth directed against movement downwards, arranged side-by-side as a unit on a single piece, forming four anchor slips pieces which protrude through respective rectangular windows cut out in a cage, so as to share a single actuator cone. Moreover, the '957 CA patent suggests arranging the anchor slips at opposite ends of each anchor unit such that each anchor piece comprises an upper teeth member and a lower teeth member rigidly joined by a bridge forming part of the same unit.
This arrangement, which is also adopted in my prior AR patent publication 53,432 A1, is currently preferred and used in the present invention since it simplifies construction and operations. However, this arrangement has drawbacks when the time comes to release the tool which become greater the more time the tool has been set down in a well, which may be a year or more after the tool was set downhole, during which both the teeth of the anchor slips and the metallic well casing become corroded and mesh together from the material point of view, to the point that the anchor slips end up jammed against the casing when the time comes to recover the tool.